(1) Field of the Invention
The present invention relates generally to dyed textile articles and, more particularly, to a method of dyeing a synthetic fiber substrate using a dyeing assistant having an amidic nitrogen adjacent to an aromatic ring.
(2) Related Technology
The use of dyeing assistants to aid in the dyeing of various fibers is well known in the art. Such assistants are sometimes used for their ability to increase dyeing efficiency. They may also be important for dyeing fibers that are otherwise difficult to dye. For example, some polyamides and polyesters are difficult to dye. In particular, among the polyamides, aromatic polyamides are difficult to dye and typically require a dyeing assistant to achieve satisfactory dyeing. The choice of dyeing assistants, however, is few. Referring, for example to the aromatic polyamides, only a handful of compounds are known as dyeing assistants. For example, three of those compounds are:
Further, while some dye assistants are commercially available, for example, CINDYE NPC (isophorone) and CINDYE C-45 are both available from Bozzetto, Inc. of Greensboro, N.C., not all dye assistants are commercially practical.
Acetophenone, by way of example, is not a practical assistant because of its adverse characteristics. For example, it has adverse effects on humans, as well as, machinery and the water supply. Somewhat similarly, CINDYE NPC, while beneficial as a dyeing assistant, is classified as an air pollutant by the Environmental Protection Agency and requires additional monitoring and reporting. Some may find that these requirements do not make the use of CINDYE NPC cost effective. Thus, the available selection of dyeing assistants is not large, and even those available leave something to be desired in terms of their overall performance on aromatic polyamides. For example, they do not result in the most efficient dyeing, nor do they allow for various depths of shade. Such shortcomings are important for several reasons.
Dyes themselves are expensive, and any unfixed dye or amount of dye used in excess creates unnecessary waste, which increases production costs and waste-treatment costs. Further, and particularly so with aromatic polyamides, the available selection of dyes is limited.
Thus what is needed is a new dye assistant, and in particular, a dye assistant that creates an improved shade choice in dyed textiles. In addition, a dye assistant is needed that allows for more efficient dyeing of textile articles, such as polyamides or polyesters, and in particular, that allows for more efficient dyeing of aromatic polyamides. Also there exits a need for a new dye assistant that creates a variety of color shades from a single dye simply by altering the pH of the dye bath.